Ansgar Kahmen

Ansgar Kahmen
University of Basel | UNIBAS · Department of Environmental Sciences

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187
Publications
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Publications

Publications (187)
Article
Understanding δ 18O and δ 2H values of agricultural products like fruit is of particular scientific interest in plant physiology, ecology, and forensic studies. Applications of mechanistic stable isotope models to predict δ 18O and δ 2H values of water and organic compounds in fruit, however, are hindered by a lack of empirical parameterizations an...
Article
• We explore needle sugar isotopic compositions (δ18O and δ13C) in boreal Scots pine (Pinus sylvestris) over two growing seasons. • A leaf‐level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict δ18O and δ13C of two hierarchical needle carbohydrate pools, acco...
Article
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Experimental: approaches to isolate drivers of variation in the carbon-bound hydrogen isotope composition (δ2 H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how 2 H-fractionations in carbohydrates differ between species. We analysed, for the first time, the δ2 H...
Article
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Conventional high-input farming systems in Europe are often regarded as unsustainable with severe environ- mental impacts on biodiversity, soils, water and climate. Low-input farming approaches, such as organic farming, have been proposed to reduce environmental impacts while further improving soil properties such as soil organic matter content and...
Article
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European beech (Fagus sylvatica) was among the most affected tree species during the severe 2018 European drought. It did not only suffer from instant physiological stress but showed severe symptoms of defoliation and canopy decline in the following year. ▪To explore the underlying mechanisms, we used the Swiss-Canopy-Crane II site and studied in b...
Article
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We compiled hydrogen and oxygen stable isotope compositions (δ2H and δ18O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ2H was more closely correlated with δ2H of xylem water or atmospheric vapour, whereas leaf water δ18O was more closely correlated with air relative humidity. This resulted from t...
Article
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Drought-associated woody-plant mortality has been increasing in most regions with multi-decadal records and is projected to increase in the future, impacting terrestrial climate forcing, biodiversity and resource availability. The mechanisms underlying such mortality, however, are debated, owing to complex interactions between the drivers and the p...
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Radial stem growth dynamics at seasonal resolution are essential to understand how forests respond to climate change. We studied daily radial growth of 160 individuals of seven temperate tree species at 47 sites across Switzerland over 8 years. Growth of all species peaked in the early part of the growth season and commenced shortly before the summ...
Article
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Intercropping is a well-established practice to enhance the yield in low-input agriculture, and beneficial microbes such as arbuscular mycorrhizal fungi (AMF) combined with plant growth promoting rhizobacteria are being used as an effective and sustainable measure to improve yields. In this study, we tested if biofertilizers can not only enhance th...
Article
Stable isotope analyses are the leading method for geographic origin determination, especially of plant-based agricultural products. Origin analysis is typically done by comparing a suspicious sample to reference materials with known geographic origin. Reference materials are usually collected at the species level, assuming different varieties of a...
Article
Full-text available
The TreeNet research and monitoring network has been continuously collecting data from point dendrometers and air and soil microclimate using an automated system since 2011. The goal of TreeNet is to generate high temporal resolution datasets of tree growth and tree water dynamics for research and to provide near real-time indicators of forest grow...
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How climate change will modify belowground tritrophic interactions is poorly understood, despite their importance for agricultural productivity. Here, we manipulated the three major abiotic factors associated with climate change (atmospheric CO 2 , temperature, and soil moisture) and investigated their individual and joint effects on the interactio...
Article
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Fraudulent food products, especially regarding false claims of geographic origin, impose economic damages of $30–$40 billion per year. Stable isotope methods, using oxygen isotopes (δ ¹⁸ O) in particular, are the leading forensic tools for identifying these crimes. Plant physiological stable oxygen isotope models simulate how precipitation δ ¹⁸ O v...
Article
Significance Oxygen and hydrogen isotope distributions in rain and snow are chemical tracers that carry information about sources and history of precipitation. This information is useful for many applications in environmental and biological sciences, but measured values are often not available for a desired time and location. We developed a user-fr...
Article
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The stable carbon isotope composition of plant tissues, commonly expressed as δ¹³C, holds a wealth of information about photosynthetic pathway, water relations and stress physiology. Crassulacean acid metabolism (CAM) is a derived form of photosynthesis that allows plants to fix carbon at a higher water-use efficiency compared to the ancestral C3 p...
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Understanding the movement of water in terrestrial ecosystems and determining the soil depths from which mature trees take up water has become an important research priority. Here we test the suitability of a dynamic 2H pulse‐labelling experiment for assessing (i) the fate of a simulated precipitation event as it moves through the ecohydrological s...
Article
Hydrogen isotope ratios of plant lipids are used for paleoclimate reconstruction, but are influenced by both source water and biosynthetic processes. Measuring 2H : 1H ratios of multiple compounds produced by different pathways could allow these effects to be separated, but hydrogen isotope fractionations during isoprenoid biosynthesis remain poorl...
Article
Significance Sound knowledge of the limits of tree hydraulic function is crucial to understand drought-induced tree mortality, although the mechanisms are difficult to study in adult trees. We explored the dynamic changes that the tree hydraulic system undergoes during the progression of a severe drought in dying adults of Norway spruce. Xylem pres...
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Alpine plants complete their seasonal phenological cycle during two to three snow-free months. Under climate change, snowmelt advances and the risk of summer droughts increases. Yet, photoperiodism may prevent alpine plants from benefiting from an earlier start of the growing season. To identify the drivers of flowering phenology in the seven main...
Article
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The start of the growing season for alpine plants is primarily determined by the date of snowmelt. We analysed time series of snow depth at 23 manually operated and 15 automatic (IMIS) stations between 1055 and 2555 m asl in the Swiss Central Alps. Between 1958 and 2019, snowmelt dates occurred 2.8 ± 1.3 days earlier in the year per decade, with a...
Article
Full-text available
The frequency of extreme weather events, such as droughts, is assumed to increase and lead to alterations in ecosystem productivity and thus the terrestrial carbon cycle. Although grasslands typically show reduced productivity in response to drought, the effects of drought on grassland productivity have been shown to vary strongly. Here we tested,...
Article
Full-text available
The exchange of gaseous elemental mercury, Hg(0), between the atmosphere and terrestrial surfaces remains poorly understood mainly due to difficulties in measuring net Hg(0) fluxes on the ecosystem scale. Emerging evidence suggests foliar uptake of atmospheric Hg(0) to be a major deposition pathway to terrestrial surfaces. Here, we present a bottom...
Preprint
Full-text available
In this study, we checked the potential of bioirrigation – defined as a process of hydraulic lift where transfer of water occurs from deep soil layers to top soil layers through plant roots. We tested this in a pigeon pea (PP) – finger millet (FM) intercropping system in a field study for two consecutive growing seasons (2016/17 and 2017/18) at two...
Article
Full-text available
Drought alters allocation patterns of carbon (C) and nutrients in trees and eventually impairs tree functioning. Elevated soil nutrient availability might alter the response of trees to drought. We hypothesize that increased soil nutrient availability stimulates root metabolism and carbon allocation to belowground tissues under drought stress. To t...
Article
Reconstructing the timing of mountain range uplift and the evolution of high-altitude plateaus is important when attempting to understand potential feedbacks between tectonics and climate at geological timescales. This requires proxies that are able to accurately reconstruct elevation during different time periods in the past. Often, the sensitivit...
Cover Page
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The cover image is based on the Research Article Improving the extraction and purification of leaf and phloem sugars for oxygen isotope analyses by Marco M. Lehmann et al., https://doi.org/10.1002/rcm.8854
Article
Full-text available
Significance Climate change increases the frequency of drought events and leads to higher variability in precipitation. Drought impairs rhizosphere (root and the root-associated microbiome) functioning in trees and leads to a reduced assimilate supply belowground. It remains unclear if rhizosphere and thus whole-tree functioning can quickly recover...
Preprint
Full-text available
The exchange of gaseous elemental mercury, Hg(0), between the atmosphere and terrestrial surfaces remains poorly understood mainly due to difficulties in measuring net Hg(0) fluxes on the ecosystem scale. Emerging evidence suggests foliar uptake of atmospheric Hg(0) to be a major deposition pathway to terrestrial surfaces. Here, we present a bottom...
Preprint
Full-text available
Drought alters allocation patterns of carbon (C) and nutrients in trees and eventually impairs tree functioning. Elevated soil nutrient availability might alter the response of trees to drought. We hypothesize that increased soil nutrient availability stimulates root metabolism and carbon allocation to belowground tissues under drought stress. To t...
Article
Full-text available
Pigeon pea (Cajanus cajan) and finger millet (Eleusine coracana) are staple food crops for millions of the rural population in Asia and Africa. We tested, in field trials over three consecutive seasons at two sites in India, an intercropping and biofertilization scheme to boost their yields under low-input conditions. Pigeon pea seedlings were rais...
Article
Full-text available
RATIONALE The oxygen isotopic composition (here shown as the δ¹⁸O value) of soluble sugars in leaves and phloem tissue holds valuable information about plant functions in response to climatic changes. However, δ¹⁸O analysis of sugars is prone to error and thoroughly tested methods are lacking. METHODS We performed three experiments to test if samp...
Article
Full-text available
Pigeon pea (Cajanus cajan) and finger millet (Eleusine coracana) are staple food crops for millions of the rural population in Asia and Africa. We tested, in field trials over three consecutive seasons at two sites in India, an intercropping and biofertilization scheme to boost their yields under low-input conditions. Pigeon pea seedlings were rais...
Article
Full-text available
Pigeon pea (Cajanus cajan) and finger millet (Eleusine coracana) are staple food crops for millions of the rural population in Asia and Africa. We tested, in field trials over three consecutive seasons at two sites in India, an intercropping and biofertilization scheme to boost their yields under low-input conditions. Pigeon pea seedlings were rais...
Preprint
Full-text available
Abstract. The frequency of extreme weather events, such as droughts, is assumed to increase leading to alterations of ecosystem productivity and thus the terrestrial carbon cycle. Although grasslands typically show reduced productivity in response to drought, their effects have been shown to vary quite dramatically. Here we tested in a two-year fie...
Article
Full-text available
In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and heat wave ever recorded. Before 2018, the 2003 millennial drought was often invoked as the example of a “hotter drought”, and was classified as the most severe event in Europe for the last 500 years. First insights now confirm that the 2018 drought event...
Article
Full-text available
Bioirrigation has been defined as the transfer of hydraulically lifted water by a deep-rooted plant to a neighbouring shallow-rooted plant which cannot access deep soil moisture. In this study, we tested if facilitative effects of bioirrigation or the competition for water dominate the interaction of two intercropped plants—deep-rooted pigeon pea (...
Poster
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In Swiss beech forests (Fagus sylvatica), the increasing frequency of extreme heat and drought events leads to increased tree mortality as well as physiological damage including crown defoliation, discoloration, and dead branches. Interestingly, we find forest stands with damaged or stressed trees next to healthy trees. Therefore, we aim to investi...
Article
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The 18O‐signature of atmospheric water vapour (δ18OV) is known to be transferred via leaf water to assimilates. It remains, however, unclear how the 18O‐signal transfer differs among plant species and growth forms. We performed a 9 h greenhouse fog experiment (relative humidity ≥ 98%) with 18O‐depleted water vapour (‐106.7‰) on 140 plant species of...
Article
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Habitats with fluctuating resource conditions pose specific challenges to plants, and they often favor a small subset of species that includes exotic invaders. These species must possess a superior ability to capitalize on resource pulses through faster resource uptake or greater resource-use efficiency. We addressed this question in an experiment...
Article
Little is known about environmental factors that mitigate or intensify drought effects on tree functioning. We hypothesized that higher nutrient availability and manipulations of the source:sink ratio can partially compensate negative drought effects when drought is not too severe, whilst too extreme drought can inhibit carbon and nutrient uptake a...
Article
The Mediterranean region is highly sensitive to climate change, particularly with regard to warming and increasing aridity. Understanding its past climate history during periods similar to the Holocene is key to understand the long-term dynamics that accompany anthropogenic climate change. Marine Isotope Stage (MIS) 11 (ca. 424–367 ka BP) is consid...
Article
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Background and aim Hydraulically lifted water can be redistributed to a neighbouring plant, a process referred to as “bioirrigation”. Facilitation of bioirrigation by beneficial microbes such as arbuscular mycorrhizal (AM) fungi that form a common mycorrhizal network (CMN) between neighbouring plants has often been suggested but is not yet well exp...
Article
Full-text available
Aims The growing demand from forest managers is to identify silvicultural practices to overcome projected water scarcity during the next decades. One solution is to mix tree species in the same stand, thereby increasing resource partitioning and minimizing competition for limited soil water. This study investigates the mixture approach for Quercus...
Article
Decreasing amounts of precipitation and more frequent dry periods will challenge temperate European forests in the future. During such dry periods, short drought-intermitting rainfall events might be the only renewing water source for trees. We investigated the effects of short drought-intermitting rainfall events on the water relations of mature i...
Article
Full-text available
Hydrogen (H) isotopes of plant organic compounds are rarely employed in ecological studies. If so, these values are interpreted as being indicative of the plant source and/or leaf water. Recent observations suggest, however, that variations in hydrogen isotope fractionation that occur during the biosynthesis of plant compounds (²H-εbio) imprint val...
Article
Full-text available
Soil respiration plays a crucial role in global carbon cycling. While the response of soil respiration to abiotic drivers like soil temperature and moisture is fairly well understood, less is known about the effects of biotic drivers, such as plant above- and belowground productivity or plant diversity, and their interactions with abiotic drivers o...
Data
Manually measured soil respiration (SR), soil temperature (ST) and soil moisture (SM). (CSV)
Data
Assimilated continuous soil moisture (SM) data set. (CSV)
Data
Cumulative soil respiration and biotic parameters. (CSV)
Data
Continuously measured (at 6 of the 19 sites) soil temperature (ST) and soil moisture (SM). (CSV)
Data
Soil respiration (SR) models per plot for each site. Both years were fitted together. The SR function (Eq 1) was fitted for each plot at each site by a constrained non-linear regression, E0 was determined over all data and thereafter kept constant (E0 = 289 K). SRref, a and b are the fitted model coefficients. RSS shows the minimized residual sum o...
Data
Modelled soil respiration (SR) data set for the 19 sites. (CSV)
Data
Assimilated continuous soil temperature (ST) data set. (CSV)
Article
We used four years of sap flow measurements to elucidate intra‐ and inter‐specific variability of gs in Larix decidua Mill. and Picea abies (L.) Karst along an elevational gradient and contrasting soil moisture conditions. Site‐ and species‐specific gs response to main environmental drivers were examined, including vapour pressure deficit, air temp...
Article
Full-text available
The water status of transpiring tree crowns depends on a hydraulic continuum from the soil matrix around roots to the sub-stomatal cavity of leaves, with a multitude of hydraulic resistances along this path. Although the stem xylem path may not be the most critical of these resistances, it had been suggested that a >50% interruption of that path by...